Optical systems and circuits require a variety of devices incorporating optical structures. For example, high capacity optical communication systems which transmit information over networks composed of optically transmissive nodes, fibers, waveguides, and the like require a high power source of optical energy that is monochromatic and spatially coherent. An ideal source for producing such optical energy is a semiconductor laser.
One known type of semiconductor laser is a broad-area semiconductor laser, which has an increased lateral dimension allowing the laser to provide a high output power. Examples of such lasers are disclosed in Fu et al., "High-Temperature Operation of InGaAs Strained Quantum-Well Lasers," IEEE Photonics Technology Letters, vol. 3, No. 4, p. 308, 1991, and J. N. Walpole et al., "High power tapered semiconductor amplifiers and lasers at 980 nm," in Proc. Conf. IEEE/LEOS Annu. Meeting, Boston, Mass., paper PD2, Nov. 1992. Broad-area lasers provide a number of advantages over other types of semiconductor lasers. For example, in addition to providing high output power, such lasers provide high reliability and a simple structure that is relatively easy to fabricate. However, a significant drawback associated with broad-area lasers is that there is no provision for the lateral confinement of the optical energy and thus known broad-area semiconductor lasers are characterized by output energies that lack a high degree of spatial coherence. Moreover, the relatively large lateral dimension of the device makes it difficult to efficiently couple the optical output to an external device such as a waveguide. As a result of these deficiencies, broad-area lasers have to date not been used in communication systems but are typically employed simply to characterize various materials or to provide a high brightness source of light.
Accordingly, it is an object of the invention to provide a semiconductor laser such as a broad-area laser whose optical output exhibits a high degree of spatial coherence and which can be efficiently coupled to an external waveguide or fiber so that it may be employed in an optical communications system.